I highly recommend against attempting to read through the entirety of Campbell's. You should put in more effort to mastering the chemistries and improving reading and math speed.
If you are bent on trying to destroy the bio section and using Campbell's. Try evaluating those topics you feel you need more thorough information on, and read those topics in Campbell's. You will hear/read an endless torrent of suggestions for what to read in Campbell's, and no doubt it will add up to 100s and 100s of pages of dense information, which is why I suggest you base what you read on your own personal feelings.
You may find this chapter breakdown by Wizi to be helpful:
http://forums.studentdoctor.net/showthread.php?t=782308
Recently I saw 1800RAW who just took the DAT recommend reading over ecology (a very manageable section of Campbell's), and well as animal form and function (a very large section that would best be picked through rather than read through completely based on time considerations).
There is also a file someone composed of a few odd chapters (18-21) with some esoteric information of possible value, that would be an easy one to read through (chromosome21's post):
http://forums.studentdoctor.net/showthread.php?t=783353
Regarding Destroyer, take the bio section with a grain, it is very specific and of questionable overall value to the DAT bio section.